A big manufacturing operation can produce 6000 to 10,000 sheets per hour, for instance thin metal sheets that are painted and dried. These sheets are stacked on pallets for shipping. The sheet stacker must take the individual sheets as they arrive at high speed and position them accurately on the top of the stack without damaging the sheets in any way.
Normally the sheets are transported at their high delivery speed on a conveyor belt that projects them against a horizontally deflectable bumper that defines the downstream end of their travel and of the pile. Thus the leading edge of the sheet butts the bumper and then the sheet settles down onto the stack.
Due to the high speed at which the sheets are transported, they strike with some force against the bumper. This can damage their leading edges. In addition the sheets can rebound somewhat so they do not drop down and form a neat stack.